Electromagnetic shielding film and circuit board

Abstract

The present invention discloses an electromagnetic shielding film and a circuit board, wherein the electromagnetic shielding film comprises a shielding layer, and the shielding layer comprises a first surface and a second surface opposite to each other; in a sliced ​​state, two points with the largest vertical distance are marked on the first surface and the second surface, and horizontal lines are drawn along the two points respectively, and the horizontal midline between the two horizontal lines is used as a reference line, and a limiting line is drawn at N microns on both sides of the reference line in the vertical direction respectively, and the parallel area between the two limiting lines is set as a limiting range, where N is less than or equal to 1 μm; wherein, for every 50 μm length, the number of wave peaks protruding from the limiting range on the first surface does not exceed 5; and / or, the number of wave peaks protruding from the limiting range on the second surface does not exceed 5. The present invention improves the flatness of the shielding layer on the shielding film to ensure that the insertion loss on the circuit board is small, and can effectively improve the reliability of signal transmission on the circuit board.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic information materials, and in particular to an electromagnetic shielding film and a circuit board. Background Art

[0002] With the rapid development of the electronics industry, electronic products are further developing towards miniaturization, lightness, and high-density assembly, which greatly promotes the development of flexible circuit boards, thereby realizing the integration of component devices and wire connections. An important indicator for evaluating the performance of flexible circuit boards is electromagnetic interference shielding (EMIShielding for short). With the integration of audio components, sensor components, etc. on mobile devices such as mobile phones, the signal transmission between these components will tend to be high-frequency and high-speed. Under the drive of high frequency and high speed, the electromagnetic interference inside and outside the components, the attenuation of signals during transmission, and the problems of insertion loss and jitter are becoming increasingly serious.

[0003] In existing circuit boards, signal shielding is performed by covering the circuit board with a shielding film to reduce electromagnetic interference and other problems. Currently, the commonly used electromagnetic shielding film mainly includes a shielding layer and a film layer, which connects the shielding layer to the ground layer of the circuit board through the film layer, and then introduces the interference charge into the ground layer of the circuit board to achieve the purpose of shielding. However, after the current electromagnetic shielding film is pressed on the circuit board, the folding of the shielding layer causes unevenness and other problems, which easily leads to relatively large insertion loss, thereby affecting the signal transmission on the circuit board. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an electromagnetic shielding film and a circuit board, by improving the flatness of the shielding layer on the shielding film to ensure that the insertion loss on the circuit board is small, which can effectively improve the reliability of signal transmission on the circuit board.

[0005] In order to achieve the above-mentioned object, an embodiment of the present invention provides an electromagnetic shielding film, comprising a shielding layer, wherein the shielding layer comprises a first surface and a second surface opposite to each other;

[0006] In the slicing state, two points with the largest vertical distance are marked on the first surface and the second surface, and horizontal lines are drawn along the two points respectively, a horizontal midline between the two horizontal lines is used as a reference line, and a limit line is drawn at N micrometers on both sides of the reference line in the vertical direction respectively, and a parallel area between the two limit lines is set as a limit range, where N is less than or equal to 1 μm;

[0007] Wherein, for every 50 μm length, the number of wave peaks on the first surface protruding out of the limiting range does not exceed 5; and / or the number of wave peaks on the second surface protruding out of the limiting range does not exceed 5.

[0008] As an improvement of the above solution, the thickness of the shielding layer is 0.1 μm to 6 μm.

[0009] As an improvement of the above solution, in the sliced ​​state, the number of breakpoints or gaps in the shielding layer does not exceed 5 per 50 μm length.

[0010] As an improvement of the above solution, the thickness range of the shielding layer is less than or equal to 1 μm.

[0011] As an improvement of the above solution, the electromagnetic shielding film further includes an insulating layer, and the insulating layer is stacked on the first surface of the shielding layer.

[0012] As an improvement of the above solution, a side of the insulating layer close to the shielding layer is a contact surface, and a ratio of a surface area to a projected area of ​​the contact surface is less than or equal to 1.5.

[0013] As an improvement of the above solution, the roughness Rz of the contact surface of the insulating layer is 1 μm to 5 μm.

[0014] As an improvement of the above solution, the thickness of the insulating layer is 3 μm to 20 μm.

[0015] As an improvement of the above solution, the electromagnetic shielding film further includes an adhesive film layer, and the adhesive film layer is stacked on the second surface of the shielding layer.

[0016] As an improvement of the above solution, a protruding structure is provided at the crest of the second surface of the shielding layer, and the protruding structure is used to pierce the adhesive film layer to connect the shielding layer to the ground layer of the circuit board.

[0017] As an improvement of the above solution, the adhesive film layer includes an adhesive layer containing conductive particles, and the shielding layer is connected to the ground layer of the circuit board through the conductive particles in the adhesive film layer.

[0018] An embodiment of the present invention further provides a circuit board, comprising a circuit board substrate and any one of the electromagnetic shielding films described above, wherein the electromagnetic shielding film is pressed together with the circuit board substrate.

[0019] Compared with the prior art, the beneficial effect of an electromagnetic shielding film and circuit board provided by the embodiment of the present invention is that: by marking two points with the largest vertical distance on the first surface and the second surface of the shielding layer in a slicing state, and drawing horizontal lines along the two points, the horizontal midline between the two horizontal lines is used as the reference line, and a limiting line is drawn at N microns on both sides of the reference line in the vertical direction, and the parallel area between the two limiting lines is set as the limiting range, N is less than or equal to 1μm; wherein, for every 50μm length, the number of peaks protruding from the limiting range on the first surface does not exceed 5; and / or, the number of peaks protruding from the limiting range on the second surface does not exceed 5. The embodiment of the present invention improves the flatness of the shielding layer on the shielding film to ensure that the insertion loss on the circuit board is small, which can effectively improve the reliability of signal transmission on the circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention;

[0021] Figure 2 is a structural schematic diagram of another preferred embodiment of an electromagnetic shielding film provided by the present invention;

[0022] Figure 3 It is a schematic diagram of an electron microscope slice of an electromagnetic shielding film provided by the present invention;

[0023] Figure 4 It is a schematic diagram of an electron microscope slice of another electromagnetic shielding film provided by the present invention;

[0024] The reference numerals are as follows:

[0025] 1. Shielding layer; 11. First surface; 12. Second surface; 13. Protruding structure; 2. Insulation layer; 3. Adhesive film layer; 10. Horizontal line; 20. Base line; 30. Limit line. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0028] In the description of this application, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0029] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood by specific circumstances.

[0030] See also Figure 1 , Figure 1 1 is a schematic structural diagram of a preferred embodiment of an electromagnetic shielding film provided by the present invention. The embodiment of the present invention provides an electromagnetic shielding film, comprising a shielding layer 1, wherein the shielding layer 1 comprises a first surface 11 and a second surface 12 opposite to each other;

[0031] In the slicing state, two points with the largest vertical distance are marked on the first surface 11 and the second surface 12, and horizontal lines 10 are drawn along the two points respectively, and the horizontal midline between the two horizontal lines is used as the reference line 20, and a limit line 30 is drawn at N micrometers on both sides of the reference line 20 in the vertical direction, and the parallel area between the two limit lines 30 is set as the limit range, and N is less than or equal to 1 μm;

[0032] Wherein, for every 50 μm length, the number of wave peaks on the first surface 11 that protrude beyond the limiting range does not exceed 5; and / or the number of wave peaks on the second surface 12 that protrude beyond the limiting range does not exceed 5.

[0033] It should be noted that insertion loss is the evaluation of the signal attenuation of the entire link from the starting point to the end point of the line, ensuring the quality of the signal during transmission. The current circuit board covered with electromagnetic shielding film has a relatively large insertion loss, partly because the unevenness of the metal layer (i.e., the shielding layer) has a certain impact on it. Studies have found that the more uneven the metal layer is, the greater its insertion loss loss will be if other conditions remain unchanged. Therefore, the embodiment of the present invention utilizes certain restrictions to constrain the flatness of the shielding layer to make its fluctuations less, which can effectively reduce insertion loss and improve signal transmission quality.

[0034] Based on this, after slicing the electromagnetic shielding film, the embodiment of the present invention observed the sample unit of every 50 μm and found that on the shielding layer 1, the number of peaks not exceeding a certain range was less than 5, regardless of the first surface 11 or the second surface 12. Therefore, the embodiment of the present invention sets the number of peaks within the preset limit range to be no more than 5, which can effectively ensure that the shielding layer 1 has good flatness, so as to effectively reduce the insertion loss of the circuit board after covering the electromagnetic shielding film.

[0035] For example, see Figure 3 , Figure 3 It is a schematic diagram of an electron microscope slice of an electromagnetic shielding film provided by the present invention. When determining the restriction range, the embodiment of the present invention marks two points with the largest vertical distance on the first surface 11 and the second surface 12 of the shielding layer 1, and draws horizontal lines 10 along the two points, and uses the horizontal midline between the two horizontal lines 10 as the reference line 20. A restriction line 30 is drawn at N microns on both sides of the reference line 20 in the vertical direction, and the parallel area between the two restriction lines 30 is set as the restriction range. Wherein, N is less than or equal to 1μm. After the restriction range is determined, for every 50μm length, the number of wave peaks protruding from the restriction range on the first surface 11 does not exceed 5; or, the number of wave peaks protruding from the restriction range on the second surface 12 does not exceed 5; or, the number of wave peaks protruding from the restriction range on both the first surface 11 and the second surface 12 does not exceed 5.

[0036] In this embodiment, if there is a protruding structure 13 on the second surface 12, the point marked when the horizontal line 10 is drawn is the point of the protruding structure 13 on the second surface 12 that is closest to the adhesive film layer 3. Figure 1 If there is no protruding structure 13, the marked point refers to the peak of the wave on the second surface closest to the film layer, such as Figure 2 shown.

[0037] The embodiment of the present invention improves the flatness of the shielding layer on the shielding film to ensure that the insertion loss on the circuit board is small, thereby effectively improving the reliability of signal transmission on the circuit board.

[0038] In another preferred embodiment, the thickness of the shielding layer 1 is 0.1 μm to 6 μm.

[0039] Specifically, according to experimental observations, within a certain range, the thicker the shielding layer 1, the better the shielding effect, and the insertion loss may also decrease accordingly. However, when the thickness of the shielding layer 1 increases to a certain extent, the improvement in its shielding effect will no longer be obvious, and the insertion loss may turn into an increase. Therefore, under the premise of ensuring the shielding effect, the embodiment of the present invention tries to set the thickness of the shielding layer 1 within a certain range to reduce the insertion loss. Exemplarily, the thickness of the shielding layer 1 is 0.1μm, 0.35μm, 0.6μm, 0.85μm, 0.7μm, 0.95μm, 1.1μm, 1.35μm, 1.6μm, 1.85μm, 2.1μm, 2.35μm, 2.6μm, 2.85μm, 3.1μm, 3.35μm, 3.6μm, 3.85μm, 4.1μm, 4.35μm, 4.6μm, 4.85μm, 5.1μm, 5.35μm, 5.6μm, 5.85μm, 6μm and / or an interval consisting of any two values.

[0040] In yet another preferred embodiment, in the sliced ​​state, the number of breakpoints or gaps in the shielding layer 1 is no more than 5 per 50 μm length.

[0041] See also Figure 4 In this embodiment, the breakpoint or gap refers to the broken notch or narrow gap of the shielding layer 1 that can be observed with an electron microscope of 2500 times or more in the sliced ​​state ( Figure 4 (center circle).

[0042] Specifically, the embodiment of the present invention further limits the number of breakpoints or gaps in the shielding layer 1. The fewer the breaks or gaps, the better the integrity of the shielding layer 1, and the lower the possibility of the signal encountering interruptions during transmission. That is, the more complete and continuous the shielding layer 1 is, the better the effect of improving the insertion loss is, which can effectively improve the quality and reliability of signal transmission and facilitate high-frequency and high-speed signal transmission.

[0043] In another preferred embodiment, the thickness difference of the shielding layer 1 is less than or equal to 1 μm.

[0044] Specifically, since the shielding layer 1 is usually in an irregular state of fluctuation and unevenness after lamination, the embodiment of the present invention further limits the thickness range of the shielding layer 1 on the basis of setting the flatness range, and sets the thickness range of the shielding layer 1 to be less than or equal to 1 μm, so as to ensure that its flatness can be well improved to a certain extent, and the insertion loss on the circuit board can be effectively reduced.

[0045] In this embodiment, the method for measuring the thickness extreme difference of the shielding layer 1 is to take samples at the raised wave crests on the first surface side of the shielding layer 1, sample the thickness of the shielding layer 1 at multiple raised wave crests, and then take the maximum thickness value and the minimum thickness value, and the difference between the two is the thickness extreme difference.

[0046] In yet another preferred embodiment, the electromagnetic shielding film further includes an insulating layer 2 , and the insulating layer 2 is laminated on the first surface 11 of the shielding layer 1 .

[0047] Specifically, the electromagnetic shielding film in the embodiment of the present invention further includes an insulating layer 2, which is stacked on the first surface 11 of the shielding layer 1. The insulating layer 2 has an insulating effect, which can ensure the shielding effectiveness of the shielding layer 1; in addition, the insulating layer 2 also has a protective effect to ensure that the shielding layer 1 is not scratched or damaged during use, thereby facilitating the maintenance of the high shielding effectiveness of the shielding layer 1.

[0048] It should be noted that the insulating layer 2 includes a PPS film layer, a PEN film layer, a polyester film layer, a polyimide film layer, a film layer formed after epoxy resin ink is cured, a film layer formed after polyurethane ink is cured, a film layer formed after modified acrylic resin is cured, or a film layer formed after polyimide resin is cured, etc.

[0049] In yet another preferred embodiment, a side of the insulating layer 2 close to the shielding layer 1 is a contact surface, and a ratio of a surface area to a projected area of ​​the contact surface is less than or equal to 1.5.

[0050] Specifically, the embodiment of the present invention further limits the ratio of the surface area of ​​the contact surface of the insulating layer 2 close to the shielding layer 1 to the projected area to be less than or equal to 1.5. The smaller the specific surface area of ​​the contact surface between the insulating layer 2 and the shielding layer 1, the better the effect on the flatness of the shielding layer 1, which can effectively improve the flatness of the shielding layer 1, thereby optimizing the insertion loss of the circuit board.

[0051] In yet another preferred embodiment, the roughness Rz of the contact surface of the insulating layer 2 is 1 μm to 5 μm.

[0052] Specifically, the embodiment of the present invention further defines the roughness Rz of the contact surface of the insulating layer 2 as 1 μm to 5 μm. Exemplarily, the roughness Rz of the contact surface of the insulating layer 2 is 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, 3 μm, 3.25 μm, 3.5 μm, 3.75 μm, 4 μm, 4.25 μm, 4.5 μm, 4.75 μm, 5 μm and / or an interval consisting of any two values. Roughness characterizes the flatness of the contact surface of the insulating layer 2 from another perspective, and the effect achieved is also to make the shielding layer 1 smoother to improve the insertion loss of the circuit board.

[0053] In another preferred embodiment, the thickness of the insulating layer 2 is 3 μm to 20 μm.

[0054] Specifically, in general, the thicker the insulating layer 2, the longer the propagation path of the electromagnetic wave therein, and the greater the attenuation. Therefore, a thicker insulating layer 2 will result in a larger insertion loss. An insulating layer 2 that is too thin may not provide sufficient electrical isolation and protection, and an insulating layer 2 that is too thick may also increase the reflection of electromagnetic waves, thereby offsetting the increase in absorption loss to a certain extent. Therefore, under the premise of ensuring the insulation performance, the embodiment of the present invention sets the thickness of the insulating layer 2 to 3μm to 20μm, and the insertion loss can be reduced at the thickness of the insulating layer 2 that is as preferred as possible. Exemplarily, the thickness of the insulating layer 2 is 3μm, 4.5μm, 6μm, 7.5μm, 9μm, 10.5μm, 12μm, 13.5μm, 15μm, 16.5μm, 18μm, 19.5μm, 20μm and / or an interval consisting of any two values.

[0055] In yet another preferred embodiment, the electromagnetic shielding film further includes an adhesive film layer 3 , and the adhesive film layer 3 is laminated on the second surface 12 of the shielding layer 1 .

[0056] Specifically, the electromagnetic shielding film in the embodiment of the present invention further includes a film layer 3, which is stacked on the second surface 12 of the shielding layer 1. The film layer 3 is arranged between the shielding layer 1 and the FPB board, and the material of the film layer 3 is generally a polymer matrix, including polyethylene terephthalate (PET), polyethylene (PE), polyvinyl alcohol (PVA), cyclic olefin copolymer (COC), etc. These materials have good flexibility, transparency and processing performance, and are ideal substrates for preparing flexible and transparent electromagnetic shielding films.

[0057] In another preferred embodiment, a protruding structure 13 is provided at the crest of the second surface 12 of the shielding layer 1, and the protruding structure 13 is used to pierce the adhesive film layer 3 to connect the shielding layer 1 to the ground layer of the circuit board.

[0058] Specifically, see Figure 1 In the embodiment of the present invention, a protruding structure 13 is provided at the crest of the second surface 12 of the shielding layer 1, so that when the electromagnetic shielding film is pressed, the adhesive film layer 3 is squeezed, and the protruding structure 13 pierces the adhesive film layer 3 and connects with the ground layer of the FPC board under the pressing force. The adhesive film layer 3 includes an adhesive layer that does not contain conductive particles, which is bonded to one side of the shielding layer 1 through the adhesive layer to cover the protruding structure 13.

[0059] In another preferred embodiment, the adhesive film layer 3 includes an adhesive layer containing conductive particles (not shown in the figure), and the shielding layer 1 is connected to the ground layer of the circuit board through the conductive particles of the adhesive film layer 3.

[0060] Specifically, in the embodiment of the present invention, when the electromagnetic shielding film is pressed together, if there is no protruding structure, the adhesive film layer 3 is provided with conductive particles, so that after pressing together, the shielding layer 1 is connected to the ground layer of the FPC board through the conductive particles.

[0061] It should be noted that the conductive particles include graphene nanosheets, carbon nanotubes (CNTs), ferroferric oxide (Fe3O4), silver nanowires (AgNWs), pure silver, silver-plated copper, silver-plated aluminum, silver-plated nickel, etc. These conductive particles can significantly improve the conductivity and electromagnetic shielding effectiveness of the film layer. For example, silver nanowires are widely used in the preparation of electromagnetic shielding films due to their excellent conductivity and transparency.

[0062] In order to firmly bind the conductive particles in the adhesive film layer 3, it is usually necessary to add an adhesive, i.e., an adhesive layer. Common adhesives include silicone, silicone fluoride, EPDM, or carbon fluoride-silicon fluoride, etc. These adhesives have good adhesion and stability, and can ensure the uniform distribution and long-term stability of the conductive particles in the adhesive film layer.

[0063] An embodiment of the present invention further provides a circuit board, which includes a circuit board substrate and the electromagnetic shielding film described in any one of the above embodiments, wherein the electromagnetic shielding film is pressed together with the circuit board substrate.

[0064] In order to demonstrate the beneficial effects of the electromagnetic shielding film and circuit board provided by the embodiments of the present invention, several embodiments and comparative examples are described below.

[0065] Example 1

[0066] In this embodiment, an electromagnetic shielding film includes a shielding layer, and the shielding layer includes a first surface and a second surface relative to each other. Wherein, within the limit range of the shielding layer, the number of wave peaks protruding from the limit range on the first surface is 4 per 50 μm length, and the number of wave peaks protruding from the limit range on the second surface is 3, and the thickness of the shielding layer of the electromagnetic shielding film is 0.5 μm. At 1 / GHz, the insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the difference between the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is obtained, △A=1dB.

[0067] Example 2

[0068] In this embodiment, an electromagnetic shielding film includes a laminated adhesive film layer, a shielding layer and an insulating layer, wherein the shielding layer includes a first surface and a second surface opposite to each other. In the limiting range of the shielding layer, for every 50 μm length, the number of wave peaks protruding from the limiting range on the first surface is 2, and the number of wave peaks protruding from the limiting range on the second surface is 3. The thickness of the shielding layer of the electromagnetic shielding film is 1.5 μm, and the number of breakpoints or gaps in the shielding layer is 3. The side of the insulating layer close to the shielding layer is a contact surface, the ratio of the surface area of ​​the contact surface to the projected area is 1.4, and the roughness Rz of the contact surface of the insulating layer is 2 μm. A protruding structure is provided at the wave peak on the second surface of the shielding layer, and the protruding structure is used to puncture the adhesive film layer to connect the shielding layer to the ground layer of the circuit board. At 5 / GHz, the insertion loss of the circuit board before and after the electromagnetic shielding film is covered is measured, and the difference between the insertion loss of the circuit board after the electromagnetic shielding film is covered and the insertion loss of the circuit board before the electromagnetic shielding film is covered is obtained. The difference △A=2.7dB.

[0069] Example 3

[0070] In this embodiment, an electromagnetic shielding film includes a laminated adhesive film layer, a shielding layer and an insulating layer, wherein the shielding layer includes a first surface and a second surface relative to each other. In the limiting range of the shielding layer, the number of wave peaks protruding from the limiting range on the first surface is 2 per 50 μm length, the number of wave peaks protruding from the limiting range on the second surface is 1, the thickness range of the shielding layer is 0.2 μm, and the thickness of the insulating layer is 6 μm. The adhesive film layer includes an adhesive layer containing conductive particles, and the shielding layer is connected and conducted to the ground layer of the circuit board through the conductive particles of the adhesive film layer. At 5 / GHz, the insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the difference in the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is obtained, △A=2.6dB.

[0071] Comparative Example 1

[0072] In this embodiment, an electromagnetic shielding film includes a shielding layer, and the shielding layer includes a first surface and a second surface relative to each other. Wherein, within the limit range of the shielding layer, the number of wave peaks protruding from the limit range on the first surface is 8 per 50 μm length, and the number of wave peaks protruding from the limit range on the second surface is 8, and the thickness of the shielding layer of the electromagnetic shielding film is 1 μm. At 5 / GHz, the insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the difference between the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is obtained, and the difference △A=5dB.

[0073] Comparative Example 2

[0074] In this embodiment, an electromagnetic shielding film includes a laminated adhesive film layer, a shielding layer and an insulating layer, wherein the shielding layer includes a first surface and a second surface opposite to each other. In the limiting range of the shielding layer, the number of wave peaks protruding from the limiting range on the first surface for every 50 μm length is 10, and the number of wave peaks protruding from the limiting range on the second surface is 13. The thickness of the shielding layer of the electromagnetic shielding film is 1.5 μm, and the number of breakpoints or gaps in the shielding layer is 8. The side of the insulating layer close to the shielding layer is a contact surface, the ratio of the surface area of ​​the contact surface to the projected area is 2, and the roughness Rz of the contact surface of the insulating layer is 10 μm. A protruding structure is provided at the wave peak on the second surface of the shielding layer, and the protruding structure is used to puncture the adhesive film layer to connect the shielding layer to the ground layer of the circuit board. At 5 / GHz, the insertion loss of the circuit board before and after the electromagnetic shielding film is covered is measured, and the difference between the insertion loss of the circuit board after the electromagnetic shielding film is covered and the insertion loss of the circuit board before the electromagnetic shielding film is covered is obtained. The difference △A=7dB.

[0075] In embodiments 1-3 of the present invention, the electromagnetic shielding film includes a laminated adhesive film layer, a shielding layer and an insulating layer, and the shielding layer includes a first surface and a second surface relative to each other. Within the limit range of the shielding layer, the number of peaks protruding from the limit range on the first surface does not exceed 5 per 50 μm length, and the number of peaks protruding from the limit range on the second surface does not exceed 5, and the thickness, flatness of the shielding layer, the specific surface area, roughness and thickness of the insulating layer are limited to the preferred range defined by the present invention, and the insertion loss of the circuit board before and after the electromagnetic shielding film is covered is measured, and the difference △A between the insertion loss of the circuit board after the electromagnetic shielding film is covered and the insertion loss of the circuit board before the electromagnetic shielding film is covered is less than 3 dB, which can effectively ensure that the insertion loss on the circuit board is small and improve the reliability of signal transmission on the circuit board.

[0076] In Comparative Example 1, the electromagnetic shielding film includes a shielding layer. Within the limitation range of the shielding layer, the number of wave peaks on the first surface protruding out of the limitation range exceeds 5 per 50 μm length, and the number of wave peaks on the second surface protruding out of the limitation range exceeds 5, which is not within the preferred range defined by the present invention. The insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the difference △A between the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is 5 dB. It can be seen that the insertion loss is high, resulting in poor reliability of signal transmission on the circuit board.

[0077] In Comparative Example 2, the electromagnetic shielding film includes a laminated adhesive film layer, a shielding layer and an insulating layer. Within the limit range of the shielding layer, the number of wave peaks protruding from the limit range on the first surface exceeds 5 per 50 μm length, and the number of wave peaks protruding from the limit range on the second surface also exceeds 5, which is not within the preferred range defined by the present invention. The number of breakpoints or gaps in the shielding layer and the specific surface area and roughness of the contact surface of the insulating layer also do not meet the preferred range defined by the present invention. The insertion loss of the circuit board before and after being covered with the electromagnetic shielding film is measured, and the change difference △A between the insertion loss of the circuit board after being covered with the electromagnetic shielding film and the insertion loss of the circuit board before being covered with the electromagnetic shielding film is 7 dB. It can be seen that the insertion loss is higher than that in Example 2, resulting in poor reliability of signal transmission on the circuit board.

[0078] To sum up, the electromagnetic shielding film prepared by limiting the flatness of the shielding layer and the specific surface area, roughness and thickness of the insulating layer contact surface as defined in the present invention can effectively reduce the insertion loss of the circuit board after being covered with the electromagnetic shielding film, and improve the reliability of signal transmission on the circuit board.

[0079] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. An electromagnetic shielding film, characterized in that: comprising a shielding layer, the shielding layer comprising opposing first and second surfaces; In the slicing state, two points with the largest vertical distance are marked on the first surface and the second surface, and horizontal lines are drawn along the two points respectively, a horizontal midline between the two horizontal lines is used as a reference line, and a limit line is drawn at N micrometers on both sides of the reference line in the vertical direction respectively, and a parallel area between the two limit lines is set as a limit range, where N is less than or equal to 1 μm; Wherein, for every 50 μm length, the number of wave peaks on the first surface protruding out of the limiting range does not exceed 5; and / or the number of wave peaks on the second surface protruding out of the limiting range does not exceed 5.

2. The electromagnetic shielding film according to claim 1, wherein The thickness of the shielding layer is 0.1 μm to 6 μm.

3. The electromagnetic shielding film according to claim 1, wherein In the sliced ​​state, the number of breakpoints or gaps in the shielding layer does not exceed 5 per 50 μm length.

4. The electromagnetic shielding film according to claim 1, wherein The thickness of the shielding layer has a maximum difference of less than or equal to 1 μm.

5. The electromagnetic shielding film according to claim 1, wherein The electromagnetic shielding film further includes an insulating layer laminated on a first surface of the shielding layer.

6. The electromagnetic shielding film according to claim 5, characterized in that A side of the insulating layer close to the shielding layer is a contact surface, and a ratio of a surface area to a projected area of ​​the contact surface is less than or equal to 1.

5.

7. The electromagnetic shielding film according to claim 6, wherein The roughness Rz of the contact surface of the insulating layer is 1 μm to 5 μm.

8. The electromagnetic shielding film according to claim 5, characterized in that The thickness of the insulating layer is 3 μm to 20 μm.

9. The electromagnetic shielding film according to claim 5, characterized in that The electromagnetic shielding film further comprises an adhesive film layer, and the adhesive film layer is laminated on the second surface of the shielding layer.

10. The electromagnetic shielding film according to claim 9, wherein A convex structure is provided at the crest of the second surface of the shielding layer, and the convex structure is used to pierce the adhesive film layer to connect the shielding layer to the ground layer of the circuit board.

11. The electromagnetic shielding film according to claim 9, wherein The adhesive film layer includes an adhesive layer containing conductive particles, and the shielding layer is connected and conducted with the ground layer of the circuit board through the conductive particles in the adhesive film layer.

12. A circuit board, characterized in that: It comprises a circuit board substrate and the electromagnetic shielding film according to any one of claims 1 to 11, wherein the electromagnetic shielding film is pressed together with the circuit board substrate.

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